Stacker crane in a warehouse

ABSTRACT

A fork-lift apparatus for use in a stacker crane has a running apparatus for traveling forward and backward and a carriage provided with a fork device and arranged for upward and downward movements by a lift apparatus for the purpose of carrying a load with the fork device to and from a desired rack in a multi-tier automatic warehouse. In particular, the carriage has at its lower region a swivel device, a swivel frame driven by the swivel device for rotating movement, and a ram fork provided in the swivel frame as driven by a drive device for movement.

TECHNICAL FIELD

The present invention relates to a stacker crane for use in a multi-tierautomatic warehouse and more particularly, to a fork-lift apparatus in astacker crane for handling roll forms of load. It also relates to amethod of controlling the fork-lift apparatus in a stacker crane forlifting and lowering various types of loads which have aperturesprovided in different regions thereof for accepting a fork(s) of theapparatus or provided in the center of a roll or cylinder form thereofmade by rolling a length of wire or a strip of sheet and also, to acontrol apparatus embodying the method.

BACKGROUND ART

A common multi-tier automatic warehouse includes a stacker crane and twoblocks of multi-tier racks disposed on both sides of a track along whichthe stacker crane travels. Each tier supports a number of loads on theirpallets. For unloading a load on its pallet from the rack, the stackercrane is anchored on the track and its carriage is elevated to the rack.Then, a fork-lift apparatus on the carriage is actuated to extend itsforks under the pallet. When the carriage is further elevated, the forkslift up the pallet with the load. The fork-lift apparatus is thenactuated to retract the forks allowing the load on the pallet to beloaded on the carriage. After the carriage is lowered by a liftingmechanism, the stacker crane travels to unload the load.

In case that the load is of a roll form having a given outer diameterand a center aperture arranged in discrete location and size, it may notappropriately be loaded and unloaded with the use of such a conventionalfork-lift apparatus in a multi-tier automatic warehouse. For smoothhandling of loads, any improved fork-lift apparatus is desired. Inaddition, the stacker crane equipped with a conventional fork-liftapparatus is relatively large in width at the carriage and its trackoccupies a considerable space in the multi-tier automatic warehouse.

If a rolled good is strapped on a pallet for ease of storage (orhandling) in a multi-pier automatic warehouse, its overall sizeincluding a pallet height and a fork accepting clearance is increasedand requires the tiers or racks to be vertically arranged at intervalsof a wider distance. This will impair the optimum use of a giveninterior space of the warehouse. Also, the time required for handling isincreased as each rolled good has to be preliminarily strapped on itspallet, thus contributing to the rise of the working cost.

When the rolled goods are identical in the size, their center aperturesinto which a fork of the stacker crane is inserted are located in thesame place. Accordingly, the goods may be loaded and unloaded with aconventional fork-life apparatus by repeating the same fork insertingaction.

In most cases, the rolled goods are different in the location of thecenter aperture and stored in discrete places in the warehouse. Hence,when one of the rolled goods is required for unloading, its centeraperture is viewed and identified by the operator of the stacker craneso that it can accept the fork successfully.

When the load to be handled is of a cylindrical shape having a centerbore for accepting the fork of a fork-lift apparatus, it is also viewedand identified by the operator for insertion of the fork into the centerbore as it is different in the size and location of the center bore fromother loads stored in the warehouse.

It is thus necessary for the operator of a conventional fork-liftapparatus to view and identify the size and location of a centeraperture of a desired load to be handled and manually control the forkfor insertion into the center aperture of the load. This action will notcontribute to the reduction of the working time during the handing ofload for storage but impairing the working efficiency.

In particular, even if the center aperture of a load into which the forkof the fork-lift apparatus is inserted has been recognized at theloading to a storage space, it has to be examined again at the unloadingfrom the same.

Also, the manual control of the fork movement by viewing may depend onskills and conditions of the operator. It is probable that excessivebrightness or illusion causes the operator to lose the visual estimationof a correct distance resulting in collision of the fork against anddamage to the load.

It is an object of the present invention, in view of the foregoingaspects, to provide a fork-lift apparatus in a stacker crane capable ofloading and unloading loads of a rolled form smoothly on the racks ortiers of a multi-tier automatic warehouse while the width of a track onwhich the stacker crane travels is minimized thus contributing to thereduction of each unit storage space in the multi-tier automaticwarehouse without sacrificing the storage amount.

It is another object of the present invention to provide a fork-liftapparatus in a stacker crane where the stable movement of a ram forkregardless of a fall moment is ensured as a counter force on the ramfork is lessened by dispersion.

It is a further object of the present invention to provide a fork-liftapparatus in a stacker crane, a method of controlling the fork-liftapparatus, and a control apparatus for implementing the method.

DISCLOSURE OF THE INVENTION

For achievement of the foregoing objects of the present invention, novelschemes have been developed. A stacker crane for carrying a load to andfrom a desired rack for storage in a multi-tier automatic warehouse hasa crane running apparatus for traveling forward and backward and acarriage arranged to support a fork-lift apparatus and driven by a liftapparatus for upward and downward movements. The fork-lift apparatus ischaracterized in that the carriage has at its lower region a horizontalswivel means, a swivel frame mounted over the horizontal swivel meansand made of an assembly of upper, lower, front, and rear members whichis open to both, left and right, sides of a track of the stacker craneand has an inner space for accepting the load, a couple of rack gearsmounted to the upper and lower members of the swivel frame respectivelyand extending lengthwisely of the swivel frame, and a ram fork mountedbetween the left and right ends in the swivel frame and comprising amain body extending between the upper and lower members of the swivelframe, a fork extending from a central region of the main body, and aplurality of pinion gears mounted to the upper and lower ends of themain body for meshing with both sides of the upper and lower rack gearsand synchronously driven by a drive means so that the ram fork cantravel throughout the swivel frame when the synchronous rotatingmovement of the pinion gears meshing with the rack gears is executed bythe drive means and simultaneously, it can be turned together with theswivel frame in the carriage by the action of the horizontal swivelmeans.

A fork-lift apparatus in a stacker crane for carrying a load to and froma desired rack for storage in a multi-tier automatic warehouse, having acrane running apparatus for traveling forward and backward and acarriage arranged to support the fork-lift apparatus and driven by alift device for upward and downward movements, is provided in that thecarriage has at its lower region a horizontal swivel means, a swivelframe mounted over the horizontal swivel means and made of an assemblyof upper, lower, front, and rear members which is open to both, left andright, sides of a track of the stacker crane and has an inner space foraccepting the load, a rack gear mounted to the lower member of theswivel frame and extending lengthwisely of the swivel frame, and a ramfork mounted between the left and right ends in the swivel frame andcomprising a main body extending between the upper and lower members ofthe swivel frame and a fork extending from a central region of the mainbody, and wires mounted over rotary members, rotatably mounted to both,front and rear, ends of the lower member and a rear end of the uppermember of the swivel frame, for joining the lower of a fork side of themain body of the ram fork to the upper of a counter fork side of thesame so that the ram fork can travel throughout the swivel frame whenthe rotating movement of pinion gears mounted to the main body of theram fork and meshed with the rack gear on the lower member of the swivelframe is executed by a drive means and simultaneously, it can be turnedtogether with the swivel frame in the carriage by the action of thehorizontal swivel means.

Also, a fork-lift controlling apparatus, according to the presentinvention, for use with a system having an input table for receiving avariety of roll-formed loads which are different in size and haveaxially extending center apertures therein into which a fork is insertedfor handling, storage racks for storage of the loads, an output tablefor removal of the loads, and a fork-lift mechanism for transferring theloads between the input table, the storage racks, and the output table,is characterized by a center detecting means for measuring the locationof the center aperture of each load placed on the input table, a memorymeans for storage of the location of the center aperture of the load, aread/write means for reading and writing the location of the centeraperture of the load on the memory means, and a fork controlling meansfor controlling the movement of the fork in accordance with the locationof the center aperture of the load so that the fork is correctlyinserted into the center aperture of the load.

The center detecting means may comprise a couple of distance sensorsprovided to sandwich the load for measuring a distance to the peripheryof the load, a traveling means for moving the distance sensors about thecross section of the load, and a transducer means for calculating thelocation of the center aperture of the load from signal outputs of thedistance sensors and movements of the same.

Also, the center detecting means may comprise a photo-electric switchmounted on the fork for detecting the present and absence of reflectedlight from front, a traveling means for moving the fork in a directionparallel to the diameter of the load, and a transducer means forcalculating the location of the center aperture of the load from asignal output and a movement of the photoelectric switch.

In action for operating the stacker crane along a track placed in amulti-pier automatic warehouse, the crane running apparatus is actuatedto run the stacker crane and simultaneously, the lift apparatus isdriven to lift (or lower) the carriage. After the carriage comes to atarget rack, the running and lifting movements are ceased. Then, when aplurality of pinion gears on the ram fork are synchronously rotated bythe drive means, the ram fork starts moving. More particularly, therotating movement of the pinion gears along two, upper and lower, rackgears provided in the swivel frame causes the ram fork to move (forward)in the swivel frame towards the rack on which a load to be unloaded isstored. Upon a fork of the ram fork reaching at a given location aftermoving into the center aperture of a roll form of the load on the rack,the forward movement of the ram fork is stopped. The lift apparatus isactuated again to lift up the carriage briefly, thus allowing the forkto hold the rolled load above the rack. Then, the ram fork is moved(backward) into the swivel frame by the action of the drive means.Accordingly, the rolled load on the ram fork is received in the swivelframe.

For carrying out the rolled load held in the carriage from thewarehouse, both the crane running apparatus and the lift apparatuses ofthe stacker crane are driven at a time so that the stacker crane runs toits home location while the carriage holding the roller load with itsram fork lowers down to the lowermost location on the stacker crane. Atthe home location of the stacker crane, the ram fork is moved (forward)to an transfer cart or table. Then, the carriage is lowered to place therolled load on the transfer cart or table. After the placement of therolled load, the ram fork is moved (backward) to remain in the swivelframe. The stacker crane stays at the home location until anothercommand is given.

For handling with the action of the ram fork a load placed on a rack ofthe opposite side of the track of the stacker crane, the swivel frame isturned 180 degrees by the action of the horizontal swivel means so thatthe front end of the fork of the ram fork comes to face the rack of theopposite side. The ram fork is then moved (forward) to the load on theopposite rack by the drive means. When the fork of the ram fork hasreached at a given location over the opposite rack, the forward movementof the ram fork is ceased. The lift apparatus is actuated for causingthe fork to hold up the load of a roll form. When the ram fork is moved(backward), the load on the fork is received in the swivel frame. Asunderstood, the turning movement of the swivel frame allows the ram forkto face in a desired direction in the carriage.

Also, the lower of the fork side and the upper of the counter fork sideof the ram fork are connected to each other by the wires which extendover the rotary members rotatably mounted to the given locations of theswivel frame and a stress exerted on the ram fork upon holding therolled load will thus be offset appropriately.

In the control method of the present invention, the location of theaperture of each load to be handled is measured, recorded, and used forcontrolling the forward movement of the fork, whereby the insertion ofthe fork into the aperture of the load will be executed without error.

The control apparatus according to the present invention allows thelocation of the aperture of each load to be recorded into the memorymeans, retrieved from the same by the retrieving means when requested,and transmitted to the fork controlling means for controlling themovement of the fork so that the fork is correctly accepted in theaperture of the load.

In action of the fork-lift apparatus which includes the input table forreceiving a variety of cylindrical loads which are different in theoverall size and the diameter of the axially extending center apertureprovided therein, storage racks for storage of the loads, an outputtable for removal of the loads stored on the racks, and a fork-liftmechanism for carrying the loads between the input table, the storageracks, and the output table, a load placed on the input table is firstsubjected to measurement of the location of its center aperture with thecenter detecting means and handled with the fork which is driven by thefork controlling means according to the location of the center aperture.As the load is held by the fork inserting into its aperture, it istransferred to a desired one of the storage racks for storage.

For transferring the load from the storage rack to the output table, thelocation of its center aperture is retrieved from the memory means bythe action of the retrieving means and used for controlling the movementof the fork. As the result, the load is readily picked up by correctinsertion of the fork into its center aperture before transferred to theoutput table.

In case of the two distance sensors are provided for measuring theirdistance from the periphery of a load to be examined through theirscanning movement, the location of the center aperture of the load isobtained by calculation of signal outputs of the two distance sensorstogether with the movement of the same in the transducer means.

When the photoelectric switch for detecting the presence and absence ofreflected light from front is provided, its movement parallel to thediameter of the load with the fork is measured and fed to the transducermeans where it is used for calculating the location of the centeraperture of the load together with a signal output of the photoelectricswitch.

As the location of the aperture center of each load (for example, adifference in height between the input table and the aperture) has beenmeasured at the receipt step of handling and recorded in the memorymeans as a compensation data, it can readily be retrieved and used forcontrolling the fork movement at any unloading step of the handling. Theaperture of the load is quickly perceived through compensating operationwith the compensation data without measuring again the location of theaperture of the load.

As the handling is automatically carried out according to the locationdata retrieved from the memory means, any collision of the fork with theload will be prevented without using visual measurement or control.

If the aperture is located at the center of a cylindrical load, it cansimply be identified by measuring the periphery of the load with thedistance sensors and photo-electric switch.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a stacker crane showing one embodimentof the present invention;

FIG. 2 is a schematic front view of the stacker crane in a multi-pierautomatic warehouse viewed from its track side;

FIG. 3 is a cross sectional explanatory view of a primary part of afork-lift apparatus according to the present invention;

FIG. 4 is a longitudinal cross sectional explanatory view of the primarypart of the fork-lift apparatus according to the present invention;

FIG. 5 is a side view of the same shown in FIG. 4;

FIG. 6 is a side view of the same shown in FIG. 5;

FIG. 7 is a cross sectional explanatory view of a primary part of afork-lift apparatus showing a second embodiment of the presentinvention;

FIG. 8 is a longitudinal cross sectional explanatory view of the primarypart of the fork-lift apparatus of the second embodiment;

FIG. 9 is a cross sectional side view of the same taken from the arrow Vof FIG. 8;

FIG. 10 is a cross sectional side view of the same taken from the arrowVI of FIG. 8;

FIG. 11 is a side view of a loading and unloading system provided with acontrol apparatus implementing a control method of the presentinvention;

FIG. 12 is a cross sectional view of the loading and unloading system;

FIG. 13 is a block diagram showing a sequence of control steps of theloading and unloading system;

FIG. 14 is an explanatory view of a primary part of a crane mechanism inthe loading and unloading system;

FIG. 15 is an explanatory view of a primary part of a center detectingmeans mounted on an input table of the loading and unloading system;

FIG. 16 is a timing chart diagram explaining the action of anothercenter detecting means;

FIG. 17 is a flow chart diagram showing a sequence of loading steps of acontrol method used with the loading and unloading system; and

FIG. 18 is a-flow chart diagram showing a sequence of unloading steps ofthe control method used with the loading and unloading system.

FIGS. 19 and 20 relate to elements in the drawings.

BEST MODE FOR EMBODYING THE PRESENT INVENTION

First Embodiment

A first embodiment of the present invention will be described referringto FIGS. 1 to 6.

A stacker crane according to the first embodiment of the presentinvention is denoted by 1 and comprises a lower saddle 3 provided with acrane traveling unit 2, two posts 4a and 4b mounted vertically on two,front and rear, near ends of the lower saddle 3, an upper saddle 5mounted to the top of the posts 4a and 4b, a carriage 7 to which afork-lift apparatus 6 is mounted, a lift drive unit 8 for lifting andlowering the carriage 7, a control/power panel 9, and other minorcomponents. The stacker crane 1 is disposed between two groups B,B ofmultiple tiers or racks in a multi-tier automatic warehouse A.

Also, provided between the two rack groups B,B is a stacker cranetraveling track C which comprises an upper rail 10a and a lower rail 10barranged opposite to each other vertically. Two wheels 11a, 11b and fourlower guide rollers 12 are rotatably mounted on the lower saddle 3 ofthe stacker crane 1 so that they travel along as engage with the lowerrail 10b. The wheel 11b is joined to the crane traveling unit 2 whichincludes a driving motor 13 and a reduction deride 14. As the wheel 11bis driven by the traveling unit 2, the wheels 11a and 11b run on thelower rail 10b.

The upper saddle 5 has four upper guide rollers 15 rotatably mountedthereon so as to sandwich the upper rail 10a. The four upper guiderollers 15 allow the stacker crane 1 to be supported at the upper by theupper rail 10a.

The carriage 7 is disposed between the two posts 4a and 4b and suspendedby wires 16 connected to the lift drive unit 8. The lift drive unit 8comprises a lift drive motor 17, a lift drum 18, and a reduction device19. As the wires 16 are rewound on and released from the lift drum 18,the carriage 7 moves upward and downward.

The fork-lift apparatus 6 of the first embodiment of the presentinvention is mounted on the carriage 7 as having the followingarrangement and function. More specifically, the carriage 7 has a swivelbearing 20 mounted to a lower inside thereo as a part of the horizontalswivel means. The swivel bearing 20 has a toothed surface 22 threaded ona movable inner ring 21 thereof. The toothed surface 22 is meshed with apinion gear 25 mounted on a rotary shaft 24 of a swivel drive motor 23.Accordingly, the inner ring 21 can rotate when the pinion gear 25 isdriven by the swivel drive motor 23.

A swivel frame 26 is mounted to the swivel bearing 20 so as to rotatetogether with the inner ring 21. The swivel frame 26 has a shape formedof assembling upper, lower, front, and rear members and opened to both,left and right, sides of the track of the stacker crane as having aninner space therein. Two, upper and lower, rack gears 27a and 27b aremounted on the inner wall of the swivel frame 26 so that they areopposite to each other at the center. The upper and lower rack gears27a, 27b are engaged with a fallen T-shaped ram fork 28 which can thusmove horizontally.

More particularly, the ram fork 28 comprises a main body 28b, a fork 28aextending horizontally from the main body 28b, and four small wheels 31rotatably mounted to the lower of the main body 28b for movement alongthe inner surface of the swivel frame 26. The ram fork 28 also has aback 28c thereof to which two rotary shafts 29a and 29b are verticallymounted for rotating movements. The two rotary shafts 29a and 29b extendto a length which is slightly greater than the distance between the tworack gears 27a and 27b and have pinion gears 30 mounted to both theupper and lower ends thereof for mesh with the rack gears 27a and 27b.

Also, side rollers 32a and 32b are rotatably mounted to both the upperand lower ends of the rotary shafts 29a and 29b. While the ram fork 28has side rollers 33 mounted to both the upper and lower ends thereof, itcan travel with the side rollers 32a, 32b, and 33 rotating along bothsides of the rack gears 27a and 27b. The ram fork 28 is supported byfour of the pinion gears 30, four of the small wheels 31, and eight ofthe side guide rollers 32a, 32b, 33 so that it travels horizontallythroughout the swivel frame 26. The overall length of the ram fork 28 isadjusted so that it can be accommodated between the left and right endsin the swivel frame 26.

The rotary shafts 29a and 29b have toothed wheels 34a and 34b fittedthereon respectively. The toothed wheel 34a of the rotary shaft 29a ismeshed with a toothed wheel 37 fitted on a rotary shaft 36 of a forkdrive motor 35 which is mounted to the back 28c of the ram fork 28. Whenthe fork drive motor 35 drives its toothed wheel 37, the two toothedwheels 34a and 34b are driven thus rotating their respective rotaryshafts 29a and 29b in synchronous relationship.

An action of unloading a rolled load from a rack b by operating thestacker crane 2 provided with the prescribed fork-lift apparatus 6 inthe multi-tier automatic warehouse will now be explained.

First, the stacker crane 1 is moved from its home position or anyposition on the track in a desired direction by actuating the travelingunit 2 in response to a command signal. Simultaneously, the carriage 7is lifted up (or lowered down) by the action of the lift drive unit 8and stopped when it comes to the rack b of the rack group B.

Then, the fork drive motor 35 on the ram fork 28 is actuated to drivethe toothed wheels 37, 34a, and 34b for synchronous rotation of therotary shafts 29a and 29b. As the two rotary shafts 29a and 29b rotate,their pinion gears 30 fitted to near the upper and lower ends rundirectly on both the rack gears 27a, 27b mounted to the upper and lowerinner walls of the swivel frame 26. Accordingly, the ram fork 28 travelsin the swivel frame 26 moving (or advancing) its fork 28a to the targetrack b. When its fork 28a has moved into the center aperture of therolled load located on the rack b and reached at a predetermined point,the ram fork 28 stops its (advancing) movement.

This is followed by brief lifting of the carriage 7 with the action ofthe lift drive unit 8 to hold with the fork 28a the rolled load abovethe rack b. When the fork drive motor 35 on the ram fork 28 is driven ina reverse direction to rotate the two rotary shafts 29a and 29bbackward, the ram fork 28 with its fork 28a holding the rolled loadmoves backward (or retracts). As the result, the rolled load on the ramfork 28 is received and accommodated in the swivel frame 26.

The rolled load held in the swivel frame 26 of the carriage 7 is thencarried out from the warehouse. More particularly, the stacker crane 1is traveled to the home position while the carriage 7 being lowered tothe lowermost place on the stacker crane 1 by the actions of thetraveling unit 2 and the lift drive unit 8 respectively. At the homeposition, the ram fork 28 is moved (or advanced) to a transfer carrieror table (not shown) and the carriage 7 is lowered down to place therolled load on the transfer carrier or table. The ram fork 28 withoutthe rolled load is then moved backward (or retracted) to remain in theswivel frame 26 of the carriage 7. The stacker crane 1 stays at the homeposition until another command signal is given.

For transferring of a rolled load from a rack b to another rack blocated on the opposite side of the stacker crane track by operating thestacker crane 1, the procedure starts with allowing the ram fork 28 toload the rolled load into the swivel frame 26 of the carriage 7.

The swivel drive motor 23 is then driven to rotate the pinion gear 25and thus the inner ring 21 of the swivel bearing 20. As the inner ring21 rotates, the swivel frame 26 is turned to 180 degrees. This actioncauses the ram fork 28 in the carriage 7 to turn 180 degrees so that itsfork 28a is directed with the front end facing the target rack b.

This action is followed by synchronous rotation of the two rotary shafts29a and 29b with the driving means of the ram fork 28. As its piniongears 30 rotate along the rack gears 27a and 27b, the ram fork 28holding the rolled load moves (or advances) towards the target rack b.Upon its fork 28a reaching a desired position on the rack b, the ramfork 28 stops its (advancing) movement. The lift drive unit 8 is thenactuated to lower the carriage 7 briefly. After the rolled load isplaced on the desired position of the rack b, the ram fork 28 is movedbackward (or retracted) to remain in the swivel frame 26 of the carriage7. The stacker crane 1 then stands by until another command signal isgiven.

The traveling, lifting, and lowering of the stacker crane 1 and theforward, backward, and rotating actions in the swivel frame of the ramfork 28 are not limited to the above mentioned controlled movements butother modifications and changes will be possible.

Second Embodiment

A second embodiment of the present invention will be described referringto FIGS. 7 to 10. Like components will be denoted by like numerals asthose in the first embodiment for simplicity.

As shown, a fork-lift apparatus 6 according to the second embodiment ofthe present invention is mounted on a carriage 7. More specifically, thefork-lift apparatus 6 has the following arrangement and function. Thecarriage 7 has a swivel bearing 20 mounted to a lower inside thereof asa part of a horizontal swivel device. The swivel bearing 20 has atoothed surface 22 threaded on the circumferential edge of a rotatableinner ring 21 thereof and a pinion gear 25 mounted on a rotary shaft 24of a swivel drive motor 23. Accordingly, the inner ring 21 can rotatewhen the pinion gear 25 is driven by the swivel drive motor 23.

A swivel frame 26 is mounted to the swivel bearing 20 so as to rotatetogether with the inner ring 21. The swivel frame 26 is formed of anassembly of upper, lower, front, and rear members having two openingsopened to both, left and right, sides of the track of the stacker craneand having an inner space. For moving the ram fork 28 in horizontaldirections lengthwisely of the swivel frame 26, a traveling device whichcomprises small wheels 31, side rollers 33, a pinion gear 37a, a drivegear 37b, and a fork drive motor 35 is disposed in the swivel frame 26together with two guide rails 27a and 27b and a rack gear 34 along whichthe ram fork 28 travels.

The guide rails 27a and 27b are mounted on both, upper and lower, innerwalls of the swivel frame 26 to extend between the left and right sideslengthwisely of the swivel frame 26. The ram fork 28 having a fallen Tshape is arranged to run horizontally along the two, upper and lower,guide rails 27a, 27b.

The ram fork 28 comprises a main body 28b and a fork 28a extendinghorizontally from the main body 28b. Four of the small wheels 31 arerotatably mounted to the lower end of the main body 28b for movementalong the inner surface of the swivel frame 26. Also, the side rollers33 are rotatably mounted to the upper and lower end of the ram fork 28for running directly along both sides of the guide rails 27a and 27b asthe ram fork 28 travels. As understood, the ram fork 28 is supported bythe small wheels 31 and the side rollers 33 for horizontal movementthroughout the swivel frame 26.

The rack gear 34 is lengthwisely mounted on the center of the lowerguide rail 27b for mesh with the pinion gear 37a mounted on a lowercenter of the ram fork 28. The pinion gear 37a is also meshed with thedrive gear 37b which is mounted above the pinion gear 37a. The drivegear 37b is connected to the fork drive motor 35 mounted on the ram fork28.

The ram fork 28 is supported by two sets of cable wires or roller chains38a and 38b for movement throughout the swivel frame 26. Moreparticularly, as shown in FIGS. 7 to 9, the swivel frame 26 has aplurality of sprockets 39a, 39b, 39c, 39d, 39e, and 39f rotatablymounted thereto so as to be located at both front and rear ends of theram fork 28. For ease of the description, one set of the roller chains38a and 38b at one side will be explained for tightening over thesprockets. The tightening of two sets of the roller chains 38a and 38bis identical.

The roller chain 38a is fixedly joined at one end to the upper front ofthe main body 28bof the ram fork 28. The other end of the roller chain38a extends over the sprockets 39a and 39b pivoted on the front and rearends of an upper region of the swivel frame 26 and the sprockets 39cpivoted on the rear end of a lower region of the same and is fixedlyjoined to the lower rear of the main body 28bof the ram fork 28.

Similarly, one end of the roller chain 38b is fixedly joined to theupper rear of the main body 28bof the ram fork 28. The other end of theroller chain 38b extends over the sprocket 39d pivoted on the upper rearof the swivel frame 26 and the sprockets 39e and 39f pivoted on thefront and rear ends of a lower region of the swivel frame 26 and isfixedly joined to the lower front of the main body 28bof the ram fork28.

An action of unloading a rolled load from a rack b by operating thestacker crane 2 provided with the prescribed fork-lift apparatus 6 inthe multi-tier automatic warehouse will now be explained.

First, the stacker crane 1 is moved from its home position or anyposition on the track in a desired direction by actuating the cranetraveling unit 2 in response to a command signal. Simultaneously, thecarriage 7 is lifted up (or lowered down) by the action of the liftdrive unit 8 and stopped when it comes to the rack b of the rack groupB.

Then, the fork drive motor 35 on the ram fork 28 is actuated to drivevia the drive gear 37b the pinion gear 37a. As the pinion gear 37a runsdirectly on the rack gear 34 of the lower guide rail 27b on the swivelframe 26, the ram fork 28 travels in the swivel frame 26 until its fork28a is moved (or advanced) to the target rack b. When the fork 28a hasmoved into the center aperture r of the rolled load R located on therack b and reached at a predetermined point, the ram fork 28 stops its(advancing) movement.

This is followed by brief lifting of the carriage 7 with the action ofthe lift drive unit 8 to hold with the fork 28a the rolled load abovethe rack b. When the fork drive motor 35 on the ram fork 28 is driven ina reverse direction to rotate the drive gear 37b and the pinion gear 37abackward, the ram fork 28 with its fork 28a holding the rolled load Rmoves backward (or retracts). As the result, the rolled load R on theram fork 28 is received and accommodated in the swivel frame 26.

While the ram fork 28 performs a series of the handling actions, itremains supported by the roller chains 38a and 38b. When the ram fork 29is loaded with the rolled load R, it is prevented from tilting to thefork 28a side as securely held with the roller chains 38a and 39b.

The rolled load R held in the swivel frame 26 of the carriage 7 is thencarried out from the warehouse. More particularly, the stacker crane 1is traveled to the home position while the carriage 7 being lowered tothe lowermost place on the stacker crane 1 by the actions of the cranetraveling unit 2 and the lift drive unit 8 respectively. At the homeposition, the ram fork 28 is moved (or advanced) to a transfer carrieror table (not shown) and the carriage 7 is lowered down to place therolled load R on the transfer carrier or table. The ram fork 28 withoutthe rolled load is then moved backward (or retracted) to remain in theswivel frame 26 of the carriage 7. The stacker crane 1 stays at the homeposition until another command signal is given.

For transferring of a rolled load from a rack b to another rack blocated on the opposite side of the stacker crane track by operating thestacker crane 1, the procedure starts with allowing the ram fork 28 toload the rolled load into the swivel frame 26 of the carriage 7.

The swivel drive motor 23 is then driven to rotate the pinion gear 25and thus the inner ring 21 of the swivel bearing 20. As the inner ring21 rotates, the swivel frame 26 is turned to 180 degrees. This actioncauses the ram fork 28 in the carriage 7 to turn 180 degrees so that itsfork 28a is directed with the front end facing the target rack b.

This action is followed by actuation of the fork drive motor 35 on theram fork 28 to rotate the drive gear 37b and the pinion gear 37a. As thepinion gear 37a runs directly on the rack gear 34, the ram fork 28holding the rolled load R travels (or advances) towards the target rackb. Upon its fork 28a reaching a desired position on the rack b, the ramfork 28 stops its (advancing) movement. The lift drive unit 8 is thenactuated to lower the carriage 7 briefly. After the rolled load isplaced on the desired position of the rack b, the ram fork 28 is movedbackward (or retracted) to remain in the swivel frame 26 of the carriage7. The stacker crane 1 then stands by until another command signal isgiven.

Third Embodiment

A third embodiment of the present invention will now be described in theform of a method of controlling the fork-lift apparatus and a fork-liftcontroller apparatus for implementing the method.

As shown in FIGS. 11, 12, 13, 14, and 15, there are an input table 1A,an output table 2A, and a rail track 3A provided on the floor. Denotedby C1 are coils made by winding a wire material into a cylindrical shapeand stored in a warehouse. The coil C1 has a center aperture C2 providedtherein and its outer diameter and width are varied depending on thethickness and length of the wire material.

Also, shown are storage blocks 41 and 42 disposed on both sides of therail track 3A and comprising a multiplicity of storage tiers 4A arrangedvertically. The two storage blocks 41 and 42 on both sides of the railtrack 3A form storage arrays 43. A center detecting means 11 is providedfor examining a difference between the reference level L1 defined by theinput table 1A and the height level of the center aperture C2 of thecoil C1 and delivering it as a compensation data L2 for position of thecenter aperture.

An ID tag 5A is provided at the lowermost of each storage array 43. TheID tag 5A comprises a rewritable data memory means 51 and a datainput/output means 52 for writing a data supplied from a fork-liftmechanism, which will be explained later, to the data memory means 51and for reading a data from the data memory means 51 and delivering itto the fork-lift mechanism.

Each of the ID tags 5A is adapted to store data for ten racks of thestorage blocks 41 and 42.

The fork-lift mechanism denoted by 6A comprises a couple of forks 61(equivalent to the ram fork 28 of the second embodiment) provided atboth, left and right, sides movable to and from the center aperture C2of the coil C1 on the rack, a fork actuating means 62 for moving theforks 61 forward and backward, a carriage 63 (equivalent to the carriage7 of the previous embodiment) movable vertically, a vertical actuatingmeans 65 (equivalent to the lift apparatus 8 of the previous embodiment)for moving the carriage 63 upward and downward throughout a crane 64, avertical movement detecting means 69 for measuring a vertical movementof the carriage 63, a cane traveling apparatus 66 (equivalent to thecrane traveling apparatus 2 of the previous embodiment) movable alongthe rail track 3A, an ID controller 67 for transmitting and receivingdata to and from the ID tags 5A, a fork controller 68 responsive to anarray data from a controller apparatus, which will be described later,for controlling the movement of the crane traveling apparatus 66 andresponsive to a tier data from the controller apparatus and acompensation data from the ID controller 67 for controlling themovements of the fork actuating means 62 and the vertical actuatingmeans 65 while monitoring the vertical movement of the carriage 63, anda power receiving means for receiving an input of motive power.

The crane traveling apparatus 66 is arranged to reach a predeterminedstorage array as counting the number of the arrays or ID tags.

The vertical movement detecting means 69 comprises a tier detectingmeans 693 including detection labels 691 allocated to the tiers or racksof each storage array and reference level detector 692 for counting thedetection labels 691 and upon the number of the counted labels 691 beingequal to the tier data, determining its position is the reference levelof a target rack 4A, a vertically extending magnetic stripe pattern 694provided on one side of the crane 64, and a compensating movementdetecting means 697 mounted on the carriage 63 for counting signalpulses given by reading the magnetic stripe pattern 694 with a magneticsensor 695 thus to calculate a movement.

The detection labels 691 may be mounted to the crane 64. Also, the racknumber detecting means 693 may be substituted by the compensatingmovement detecting means 697.

The controller apparatus is provided for controlling the foregoingcomponents in a sequence of orders as denoted by 9A and comprises aninput means 91 for receiving loading and unloading data, an addressmemory means 92 for recording a combination of storage array data andtier data of each stored coil C1 as an address data, data input/outputmeans 93 responsive to the loading and unloading data for reading andwriting of data on the address memory means 92, and a data transfermeans 94 for transmitting both the array data and tier data to thefork-lift mechanism 6A.

The address memory means 92, data input/output means 93, and forkcontroller 68 are identical to a memory means, a read/write means, and afork control means specified in claims 7 and 8 of this application.

Both a loading action and an unloading action with the above arrangementwill be explained referring to FIGS. 17 and 18. The explanation startswith initial steps of the loading action for accepting a load.

When the input means 91 receives a loading command, it starts accessingthe address memory means 92 for searching an unoccupied rack. Both arrayand tier data of the unoccupied rack are then released from the datatransfer means 94. Upon receiving the two data from the data transfermeans 94, the fork controller 68 stores them as a record and instructsthe crane traveling apparatus 66 to travel to the input table 1A. Afterthe reference level L1 of the input table 1A is measured, a differencebetween the reference level L1 and the level of the center aperture C2of the coil C1 is calculated by the center detecting means 11 and storedas the compensation data L2.

The forks 61 are then lifted up from the reference level by a distancedefined by the compensation data L2 so that one of them comes to theheight of the center aperture C2 of the coil C1. The fork actuatingmeans 62 is actuated to move the fork 61 forward for insertion into thecenter aperture C2 of the coil C1.

Then, the vertical actuating means 65 is driven to move the carriage 63upwards and thus lift up the coil C1 from the input table 1A. The forkactuating means 62 is started again to move the fork 61 backward as isfollowed by lowering the carriage 63 to its original location with thevertical actuating means 62.

Succeeding steps of the loading action for storage of the load will nowbe explained.

The crane traveling apparatus 66 is actuated in response to the storagearray data of the coil C1 so that it travels to a corresponding arraylocation.

As the crane traveling apparatus 66 has arrived at the array location,the compensation data is transmitted via the ID controller 67 to the IDtag 5A of the array 43. The compensation data received by the ID tag 5Ais then written by the data input/output means 51 to a correspondingaddress in the data memory means 52. This writing action allows previousdata in the address to be deleted automatically.

The vertical actuating means 65 is driven by the tier detecting means693 of the vertical movement detecting means 69 for lifting to thereference level L3 of the storage rack 4A of the tier defined by thetier data. The vertical actuating means 65 is then driven by thecompensating movement detecting means 697 for further upward movementthrough a distance of L4 (>L2) so that the bottom of the coil C1 ishigher than the top of the storage rack 4A. The fork actuating means 62is driven to move the fork 61 forward and then, the fork 61 is loweredby a distance of L4-L2 so that its center comes to a position which ishigher by L2 of the compensation data than the reference level L3. Asthe result, the coil C1 is placed directly on the storage rack 4A asreleased from the fork 61.

The fork actuating means 62 is driven to move the fork 61 backward andthen, the vertical actuating means 65 is driven for downward movement tothe original height position. During the loading action, the majorvertical movement or tier accessing movement of the vertical actuatingmeans 65 is controlled by a signal of the tier detecting means 693 whilethe minor vertical movement or L4 and L2 associated movement at thetarget tier of the same is controlled by a signal of the compensatingmovement detecting means 697. The loading action is now completed.

The unloading action will be explained starting with steps of removal ofa load.

When the input means 91 receives an unloading command, it startsaccessing the address memory means 92 to identify the storage rack 4Awhere a target coil C1 is stored. The storage array data and tier dataof the rack 4A are transmitted by the data transfer means 94 to the forkcontroller 68 of the fork-lift mechanism 6A.

Then, the crane traveling apparatus 66 is actuated according to thearray data for traveling to the storage array 43 of the coil C1.

When the crane traveling apparatus 66 has arrived at the array location,the compensation data L2 for the coil C1 stored in a correspondingaddress of the data memory means 51 in the ID tag 5A of the array 43 isread out by the ID controller 67 in cooperation with the datainput/output means 52.

The vertical actuating means 65 is driven in response to the tier datafor upward movement to the reference level L3 of the storage rack 4A.The vertical actuating means 65 is further moved upward by L2 of thecompensation data so that the fork 61 comes to the center aperture C2 ofthe coil C1. The fork actuating means 62 is then driven to move the fork61 forward for insertion into the center aperture C2 of the coil C1.

After the upward movement is briefly repeated to lift up the coil C1from the storage rack 4A, the fork actuating means 62 is driven to movethe fork 61 backward as is followed by the lowering movement with thevertical actuating means 65 to the original position.

Steps of the unloading action for releasing the load will now beexplained.

The crane traveling apparatus 66 is driven for traveling to the outputtable 2A. The vertical actuating means 65 is then driven for upwardmovement to the reference level L5 of the output table 2A. After afurther upward movement of L4 (>L2) for lifting up the coil C1 so thatits bottom is higher than the top of the output table 2A, the forkactuating means 62 is driven to move the fork 61 forward. Then, the fork61 is lowered by L4-L2 so that it comes to a location higher by L2 ofthe compensation data from the reference level L5. As the result, thecoil C1 is placed directly on the output table 2A as released from thefork 61. The fork actuating means 62 is driven again to move the fork 61backward and the vertical actuating means 65 is driven for downwardmovement to the original position.

The unloading action is now completed.

It is desirable that the input table 1A, the storage rack 4A, and theoutput table 2A are identical to each other in the compensation data ofL2 which extends from their surface to the center line of the centeraperture C2 of the coil C1. In case that the compensation data L2 is notidentical, it can easily be corrected by adjusting the components of thefork-lift mechanism.

The center detecting means 11 may employ distance sensors assembled inthe following arrangement.

More specifically, the center detecting means 11 comprises an upperdistance sensor 111 distanced upwardly by H1 from the reference level L1of the input table 1A for detecting a distance from the top of the coilC1, a lower distance sensor 112 distanced downwardly by H2 from thereference level L1 of the input table 1A for detecting a distance fromthe bottom of the coil C1, a scanning means 113 for scanning with boththe distance sensors 111 and 112, and a transducer circuit 114 forcalculating and delivering the compensation data L2. In action, thedistance H3 between the upper distance sensor 111 and the top of thecoil C1 is measured by scanning the top of the coil C1 placed on theinput table 1A and the distance H4 between the lower distance sensor 112and the bottom of the coil C1 is measured by scanning the bottom of thesame.

The scanning means 113 and transducer circuit 114 are identical to atraveling means and a transducer means defined in claim 7 of thisapplication.

Using the four measurements H1, H2, H3,and H4, the compensation data L2which represents a distance of the center line of the center aperture C2from the reference level L1 is calculated from Equation 1 as expressedbelow. ##EQU1##

In the above arrangement, the distance sensors are disposed above andbeneath the coil C1. However, the distance sensors may be arranged atboth, left and right, sides of the coil C1 with equal success formeasuring horizontal distances to the center line of the center apertureC2 by scanning.

Also, the distance sensors may be substituted by a combination of thecompensating movement detecting means 697, the vertical actuating means65, and a photoelectric switch 118 mounted on the fork 61 as shown inFIG. 14.

In this case, the further upward movement of the carriage is executedafter the reference level is measured by a reference level detectingmeans.

Hence, the vertical actuating means 65 and compensation movementdetecting means 697 correspond to a traveling means and a transducermeans defined in claim 8.

This movement is followed by examining with the photo-electric switch118 whether or not there is a reflective object in the front of the fork61 and counting pulses of the magnetic sensor.

As shown in FIG. 16, an N1 number of pulses are counted until the fork61 reaches the center aperture C2 of the coil C1, N2 pulses are countedduring scanning of the center aperture C2 before a reflected light isdetected, and N3 pulses are counted until it reaches the top of the coilC1 where the reflected light is no more detected. Using the pulsenumbers N1, N2, and N3, and a rate of resolution (K mm/pulse) of themagnetic sensor, the compensation data L2 which represents a distance ofthe center line of the center aperture C2 of the coil C1 from thereference level L1 is then calculated from Equation 2 as expressedbelow. ##EQU2##

It is understood that the two above examples of the center detectingmeans 11 are illustrative but not of limitation.

More preferably, two or more of the center detecting means 11 may beprovided for a fail-safe function where one is applicable when the otheris defective or out of order.

It is desirable for optimum action of the fork-lift mechanism 6A toverify at an initial stage that the carriage remains at the originallevel, that the fork 61 stays at its retracted state, and that no coilC1 is held in the fork-lift mechanism 6A, and to examine whether or notthe coil is placed on the input or output table.

According to the embodiment of the present invention, a distance data ofthe center aperture C2 of the coil C1 from the upper surface of theinput table is measured and recorded at the loading action. It can beretrieved and used for identifying the height level of the coil C1during the unloading action without being measured again. Accordingly,the unloading of the coil C1 will readily be implemented while anycollision of the fork against the coil C1 being avoided.

For the purpose, there are provided only the means for measuring andrecording the location of the center aperture C2 of the coil C1 at theloading action.

In the embodiment, the center aperture of a load is measured at theinitial stage of the loading action as is not informed. If anyappropriate data, e.g. a radius, which is used as a compensation data atthe receiving step is given together with the ID number of the load forease of handling, the center detecting means 11 may be eliminated.

FEASIBILITY FOR INDUSTRIAL APPLICATIONS

As set forth above, the present invention allows any load of a rolledform to be smoothly loaded to or unloaded from a desired tier of amulti-tier automatic warehouse by controlling the traveling movement ofthe stacker crane, the lifting and lowering movements of the carriage,and the forward and backward movements of the ram fork.

The ram fork is arranged for movements forward and backward in a swivelframe on the carriage by means of rack and pinion gears, carrying therolled load to and from the swivel frame for storage on a desired rackwithout using an extensive length of the fork member. Also, the carriagecontains a swiveling means for turning the ram fork in the swivel framethrough 180 degrees, thus allowing the rolled load to be easilytransferred from one to the other of the two tier blocks disposed onboth sides of a track of the stacker crane. Also, the load on thestacker crane can be loaded to and unloaded from any rack of either ofthe left and right blocks.

As no pallet is required, its thickness and a margin for the fork aredisregarded. This allows the amount of storage to be increased and theavailable space in a warehouse to be utilized at optimum. During thehandling, there is no time for loading a load to a pallet and theoverall procedure will be shortened thus decreasing the cost.

According to the present invention, the center of swivel movement is atthe center of the carriage, i.e. the swivel frame rotates about itsgravity center. This allows the effect of inertia force to be minimized.Hence, the speed of swivel movement will be increased and the cycle timefor loading and unloading of loads will be decreased.

The ram fork in the swivel frame is movably supported by the cable wireswhich extend from the lower end of the fork side of the ram fork to theupper end of the counter fork side of the same via the rotary memberpivoted on specified regions of the swivel frame. This allows any stressexerted on the ram fork when a load is carried to be offset, thusensuring constant stable movements of the ram fork.

According to the control method of the present invention, the movementof the fork is controlled by a location data of the center aperture of aload which is to be carried. Hence, the load will readily be carried toand from a warehouse without being monitored by the operator nor havingany possibility of colliding with the fork. The handling of the loadswill thus increased in the operational reliability and efficiency.

For implementing the above method, the control apparatus of the presentinvention includes a memory means for recording the location data of thecenter aperture of each load, a retrieving means for reading therecorded location data, and a fork controlling means for controlling themovement of the fork with the location data.

In case of a load to be loaded is formed of a cylindrical shape having acenter aperture therein into which the fork is inserted for carrying,the location of its center aperture is measured and recorded at thebeginning of loading. For unloading of the load, the location of itscenter aperture is retrieved and used for controlling the movement ofthe fork. Accordingly, the control apparatus like the control methodwill be enhanced in the operational reliability and efficiency.

As the location of the center aperture of a load is simply measured byscanning with a distance sensor over the periphery of the load, theforegoing function of the control apparatus will be performed with easeand certainty.

The control apparatus may be implemented in which the center aperturelocation is measured by moving a photoelectric switch for detecting thepresence or absence of reflected light.

With the use of a combination of the above devices, the controlapparatus will be further increased in the operational reliability.

As described, the control method and apparatus according to the presentinvention allow the fork to be inserted into the center aperture of aload readily and accurately for loading to and unloading from awarehouse.

We claim:
 1. A fork-lift apparatus in a stacker crane for carrying aload to and from a desired tier for storage in a multi-tier automaticwarehouse, having a crane running apparatus for traveling forward andbackward and a carriage arranged to support the fork-lift apparatus anddriven by a lift apparatus for upward and downward movements,characterized in that the carriage has at its lower region a horizontalswivel device, a swivel frame mounted over the horizontal swivel deviceand made of an assembly of upper, lower, front and rear members which isopen to both, left and right, sides of a track of the stacker crane andhas an inner space for accepting the load, a couple of rack gearsmounted to the upper and lower members of the swivel frame respectivelyand extending lengthwisely of the swivel frame, and a ram fork mountedbetween left and right ends in the swivel frame and comprising a mainbody extending between the upper and lower members of the swivel frame,a fork extending from a central region of the main body, and a pluralityof pinion gears mounted to the upper and lower ends of the main body formeshing with both sides of the upper and lower rack gears andsynchronously driven by a drive means mounted on the main body so thatthe ram fork can travel throughout the swivel frame when the synchronousrotating movement of the pinion gears meshing with the rack gears isexecuted by the drive means and simultaneously, it can be turnedtogether with the swivel frame in the carriage by the action of thehorizontal swivel device.
 2. A fork-lift apparatus in a stacker cranefor carrying a load to and from a desired tier for storage in amulti-tier automatic warehouse; having a crane running apparatus fortraveling forward and backward and a carriage arranged to support thefork-lift apparatus and driven by a lift device for upward and downwardmovements, characterized in that the carriage has at is lower region ahorizontal swivel device, a swivel frame mounted over the horizontalswivel device and made of an assembly of upper, lower, front, and rearmembers which is open to both, left and right, sides of a track of thestacker crane and has an inner space for accepting the load, a rack gearmounted to the lower member of the swivel frame and extendinglengthwisely of the swivel frame, and a ram fork mounted between leftand right ends in the swivel frame and comprising a main body extendingbetween the upper and lower members of the swivel frame and a forkextending from a central region of the main body, and wires mounted overrotary members, rotatably mounted to both, front and rear, ends of thelower member and a rear end of the upper member of the swivel frame, forjoining the lower of a fork side of the main body of the ram fork to theupper of a counter fork side of the same so that the ram fork can travelthroughout the swivel frame when the rotating movement of pinion gearsmounted to the main body of the ram fork and meshed with the rack gearon the lower member of the swivel frame is executed by a drive means andsimultaneously, it can be turned together with the swivel frame in thecarriage by the action of the horizontal swivel device.
 3. A fork-liftcontrolling apparatus for use with a system having an input table forreceiving a variety of roll-formed loads which are different in size andhave axially extending center apertures therein into which a fork isinserted for handling, storage racks for storage of the loads, an outputtable for removal of the loads, and a fork-lift mechanism fortransferring the loads between the input table, the storage racks, andthe output table, characterized by a center detecting means formeasuring the location of the center aperture of each load placed on theinput table, a memory means for storage of the location of the centeraperture of the load, a read-write means for reading and writing thelocation of the center aperture of the load on the memory means, and afork controlling means for controlling the movement of the fork inaccordance with the location of the center aperture of the load so thatthe fork is correctly inserted into the center aperture of the load, thecenter detecting means comprising a couple of distance sensors providedto sandwich the load for measuring a distance to the periphery of theload, a traveling means for moving the distance sensors about the crosssection of the load, and a transducer means for calculating the locationof the center aperture of the load from signal outputs of the distancesensors and movements of the same.
 4. A fork-lift controlling apparatusfor use with a system having an input table for receiving a variety ofroll-formed loads which are different in size and have axially extendingcenter apertures therein into which a fork is inserted for handling,storage racks for storage of the loads, an output table for removal ofthe loads, and a fork-lift mechanism for transferring the loads betweenthe input table, the storage racks and the output table, characterizedby a center detecting means for measuring the location of the centeraperture of each load placed on the input table, a memory means forstorage of the location of the center aperture of the load, a read/writemeans for reading and writing the location of the center aperture of theload on the memory means, and a fork controlling means for controllingthe movement of the fork in accordance with the location of the centeraperture of the load so that the fork is correctly inserted into thecenter aperture of the load, the center detecting means comprising aphotoelectric switch mounted on the fork for detecting the presence andabsence of reflected light from front, a traveling means for moving thefork in a direction parallel to the diameter of the load, and atransducer means for calculating the location of the center aperture ofthe load from a signal output and a movement of the photoelectricswitch.